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Discussion Starter #1
Anyone out there who's gone from a 285/70/17 to a 315/70/17 notice a drop in power?
 

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I went from stock to 315's and felt a big drop in the low end.
 

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It is because you are gearing the truck higher by putting bigger tires on it. A larger tire travels further for every revolution. That is exactly what a transmission does. Each gear changes how far in distance the truck travels for every revolution of the driveshaft or crank shaft.
It takes more power or torque to move a vehicle with larger tires because you are asking it to move further for every revoulution. It is like taking 3.73's out and putting a 3.08 in there and keeping the stock tires. If you keep your big tires and put 4.10s in it, then you will get the bottom end back in it.
 

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I notice a small change, but it is hard to quantify. There is more resistance both from the air and the ground along with the diameter difference. I lose about 1/2 mile per gallon in mileage when switching between 285 and 315. So the simple anwer is yes.
You need someone who has 1/4 mile times with both tires and then calculate the difference.
 

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You're also adding rotational unsprung mass, which can be like adding several hundred pounds to the truck's weight. The lack of performance is not just gear ratios but also decreasing your torque / weight ratio. The effect is very real and very annoying. You could do an intake / exhaust / power programmer to get some of that acceleration back.
 

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These trucks have so much power and torque you will not notcie that much of a difference. However i would not put toyo mt's on it. my truck had 315/75R16 Cooper St's on it when i bought it and then i went to the toyo's in the same size and the difference in weight between the coopers and the toyo's was very noticable. The toyo's have a very thick sidewall and they weight much more than the coopers. I noticed the difference.
 

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It is because you are gearing the truck higher by putting bigger tires on it. A larger tire travels further for every revolution. That is exactly what a transmission does. Each gear changes how far in distance the truck travels for every revolution of the driveshaft or crank shaft.
It takes more power or torque to move a vehicle with larger tires because you are asking it to move further for every revoulution. It is like taking 3.73's out and putting a 3.08 in there and keeping the stock tires. If you keep your big tires and put 4.10s in it, then you will get the bottom end back in it.
OR you can load the 120 tune and get more bottom, mid and top:D
 

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Discussion Starter #9
Hey Montana LB7, what did you think of the cooper ST compared to the Toyo? I'm thinking about going to the ST in a 33/12.50/17. Although the Cooper is probably one of the most popular tires here in Bozeman. Not many choices in this size.
 

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I'm quite satisfied after putting my 315s on. With stock tires I was always chirping them or even smokin' them if I got excited. Now I'm very happy with the balance between power and control. Please note I do run with a Bully Dog Pwr Pup on the medium setting.
 

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bobd,

They are ok tires, i realy like toyo tires, i think that they are a great tire. I also like the new pro-comp xtreme AT which is also made in a 33x12.5r17. Pro-Comps are made by Cooper so it is the same quality. Say away from Big-O tires i really do not like them at all even though i like the local big o here in Bozeman. If you want coopers or toyo's go see corey at interwest tire in belgrade, tell him scott sent you and he will take care of you. If you want pro-comps, PM me and i will let you know more about them.

Scott
 
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